Juan Mata scored the only goal as Manchester United recorded an underwhelming 1-0 victory over FC Rostov on Thursday to reach the Europa League quarterfinals.

Mata struck 20 minutes from the end of a subdued game, completing a 2-1 aggregate win that sent United into the last eight of Europe's second-tier club competition for the first time since 1985.

But victory came at the cost of an injury to world-record signing Paul Pogba, who left the fray with an apparent hamstring injury early in the second half at an unseasonably cold Old Trafford.

United manager Jose Mourinho said Pogba's injury was due to "fatigue" and hit out at unnamed "enemies" in an apparent reference to his side's jam-packed fixture schedule.

"Normally the enemies should be Rostov, but we have a lot of enemies," Mourinho told BT Sport.

"It's difficult to play Monday with 10 men (against Chelsea). It's difficult to play now. It's difficult to play 12 o'clock on Sunday (against Middlesbrough). We have a lot of enemies."

United, who have never previously won the Europa League, will discover their last-eight opponents in Friday's draw in Nyon.

Mourinho's men are seeking to add the trophy to the League Cup they won last month and have the extra incentive of knowing it will yield a place in next season's Champions League.

Mourinho kept faith with the back three he had deployed in Monday's 1-0 FA Cup defeat at Chelsea.